1. Field of the Invention
Directional light modulation, 3D displays, emissive micro displays, 2D/3D autostereoscopic switchable displays.
2. Prior Art
In some switchable 2D/3D displays a directional backlight is necessary to operate the display in different display modes. In a 2D display mode, a backlight with uniform illumination and large angular coverage is required to display a single image with spatial light modulators (such as liquid crystal displays (LCD)). In a 3D display mode, a backlight with uniform illumination and multiple illumination directions is required to display images of the same scene from different directions by utilizing some combination of spatial multiplexing and temporal multiplexing in the spatial light modulator.
In both 2D and 3D modes, the light that comes from the directional backlight is usually processed by a directionally selective filter (such as diffractive plate, a holographic optical plate etc.) before it reaches the spatial light modulator pixels to expand the light beam uniformly while keeping its directionality.
Currently available directional light modulators are a combination of an illumination unit comprising multiple light sources and a directional modulation unit that directs the light emitted by the light sources to a designated direction (see FIG. 3). An illumination unit is usually combined with an electro-mechanical movement device such as rotating mirrors or rotating barriers (see U.S. Pat. Nos. 6,151,167, 6,433,907, 6,795,221, 6,803,561, 6,924,476, 6,937,221, 7,061,450, 7,071,594, 7,190,329, 7,193,758, 7,209,271, 7,232,071, 7,482,730, 7,486,255, 7,580,007, 7,724,210, and 7,791,810 and U.S. Patent Application Publication Nos. 2010/0026960 and 2010/0245957), or electro-optical device such as liquid lenses or polarization switching (see FIG. 1 and FIG. 2 and U.S. Pat. Nos. 5,986,811, 6,999,238, 7,106,519, 7,215,475, 7,369,321, 7,619,807 and 7,952,809).
In both electro-mechanically and electro-optically modulated directional light modulators there are three main problems:
1. Speed: When electrical energy is used to create mechanical movement or optical change, the movement or change is not achieved instantaneously. Usually a type of acceleration, deceleration and stabilization has to be achieved to reach the desired mechanical or optical state. The speed of these operations usually takes up a significant portion of the frame time that reduces the efficiency and limits the achievable display brightness.
2. Volumetric thickness of the device: Both of these methods need a distance between the light source and directional modulation device to work with, which increases the total thickness of a display.
3. Light loss: Coupling light on to a moving mirror assembly or using a liquid lens with adjustable focal length creates a light loss on the order of 50% to 90% which in turn requires more power consumption to compensate for the light loss, and creates heat in the system that has to be eliminated by a cooling method.
In addition to being slow, bulky and optically lossy, the prior art directional backlight units need to have narrow spectral bandwidth, high collimation and individual controllability for being combined with a directionally selective filter for 2D-3D switchable display purposes. Achieving narrow spectral bandwidth and high collimation requires device level innovations and optical light conditioning, increasing the cost and the volumetric aspects of the overall system. Achieving individual controllability requires additional circuitry and multiple light sources, increasing the system complexity, bulk and cost.
It is therefore an objective of this invention to introduce a spatio-optical light modulator that overcomes the drawbacks of the prior art, thus making it feasible to create 3D displays that provide practical volumetric and viewing experience. Additional objectives and advantages of this invention will become apparent from the following detailed description of a preferred embodiment thereof that proceeds with reference to the accompanying drawings.